1. Field of the Invention
The present invention concerns an anchoring device including a cylindrical hollow body having a first edge, a second edge, a forward end having attachment means for applying a traction force to the body, a backward end opposite to the forward end, and fluke means for improved anchorage properties.
The term cylindrical body used herein is intended to include any kind of cylindrical body, i.e., not only a straight circular cylinder body, but also such cylinders that have a non-regular figure as its base, or an axis that is not perpendicular to the base.
The anchoring device is primarily, but not exclusively, intended for permanent or long-time anchorage, such as for anchoring oil rigs.
2. Description of Background Art
A plurality of different anchoring devices are known since long ago for anchoring ships and smaller vessels, such as yachts, as well as for anchoring mooring buoys and floating platforms, such as oil rigs. When it comes to anchoring floating landing stages or jetties, heavy and cumbersome molded concrete blocks are frequently used having a steel eye molded into the block for attachment of an anchor chain or wire. Since a solid body of concrete, having a specific gravity of 1.8-2.5 depending, a.o., on the ballast material, looses about 40% of its effective weight when it is immersed in water, it must be made excessively big and heavy in order to achieve its desired anchorage properties, or, it must be shaped such that its shape provides improved anchorage properties.
An anchoring device made of steel, having a specific gravity of typically 7.8, can be made much smaller for a certain weight, and it can easily be shaped for improved anchorage properties, such as being provided with sheet metal projections as fluke means. One such anchoring device having a cylindrical body in the shape of a straight circular cylinder is marketed in Sweden under the trade name "P-ringen" (the P-ring). It consists of a circularly bent length of strip iron, the ends of which are welded together to form a closed ring. A steel eye is welded to the outer circumference of the ring for attachment of a chain or wire. Symmetrically about the eye, four flukes are welded to the ring, two at one axial end of the cylinder and two at the opposite axial end thereof. The flukes are slightly bent so as to be directed towards the direction of traction in a chain or wire attached to the eye. This is supposed to improve the anchorage by making the forward end of the device dig into the bottom.
A problem encountered, however, is that heavy sea, combined with heavy traction in the chain or wire, tends to raise the forward end of the ring with the flukes from the bottom, thus leaving only the back end of the ring in bottom contact.